In a typical aircraft manufacturing line, structural subassemblies (e.g. wing sections) are built up of elementary parts (e.g. spars, ribs, skins) by the installation of mechanical fasteners such as rivets into precisely drilled holes. All current manufacturing processes include drilling, fastening and other operations on these elementary parts to build a subassembly. Assemblies are generally built on jigs. Manufacturing techniques range in complexity from stationary jigs staffed by workers with hand tools to fully automated assembly lines equipped with monumental robotic installations.
In an illustrative example, an aircraft manufacturing line uses a drilling system. The drilling system enables tools to interface with airplane parts. Once an interface is set up, operating an interfacing tool becomes possible to perform particular drilling operations on a corresponding airplane part.
Typically, there are three existing types of drilling processes, each with its own drawbacks:                1. Manual tools        2. Semi-automated drilling tools        3. Monumental Machines        
Manual drilling with hand tools is highly labor intensive and prone to defect generation. Hole positions are defined by hard tooling such as drill templates. The template installation process is not very precise and can induce positional accuracy errors. These are subject to wear, requiring periodic inspection and recertification. If the design of the aircraft changes or a new variant is developed, new tooling may be needed. In a manual drilling process, each hole is processed by hand in at least four discrete steps: pilot drilling, full size drilling, reaming and countersinking. This is a labor intensive, defect prone process. At each step, the operator can generate a defect. Common defects include perpendicularity, scratches inside the bore of the hole, over depth countersinks, and use of the wrong size drill bit.
Various semi-automated tools exist to address some limitations of fully manual processes such as the four-step drilling sequence. One example is the advanced drilling unit (ADU) from Seti-Tec of Lognes, France. Like manual drilling tools, these tools too, are positioned using application-specific drilling jigs which should be remade if the design of the aircraft changes or the drilling tools should be used on a different component or aircraft model. Semi-automated tools suffer the same template positioning errors as manual drilling processes. As an improvement over simple hand drills, this type of machine can drill, ream and countersink in one shot, largely removing the operator from the hole quality equation. The process is single-operation focused (drills cannot route panels). It is still labor intensive with one-to-one or sometimes one-to-several corresponding operators-to-drills.
Monumental robotic installations are expensive and are often heavy enough to need a specially prepared foundation to support the weight of the machine. The fixed nature of the machines make factory reconfiguration impossible. These machines come with long lead times on the order of years, do not scale with increases in production volumes, and are costly to maintain. These machines are typically designed to process a single assembly for the life of the machine. There is little scope for reconfiguration to support manufacturing different models of product. Highly specialized personnel should be hired and trained to operate and maintain these large, complex pieces of equipment.